Method and apparatus for etching disk-like member

ABSTRACT

Disclosed are a method and apparatus for etching disk-shaped members, especially a method and apparatus for etching semiconductor wafers. In a method wherein wafers ( 30 ) are rotated and etched in an etching chamber ( 12 ) which is filled with an etching solution, a non-rotating cell plate ( 26 ) is disposed between two rotating wafers ( 30 ). In an etching apparatus wherein multiple wafers ( 30 ) are supported and rotated by a rod ( 16 ), the cell plate ( 26 ) is disposed between each two wafers ( 30 ). The cell plate ( 26 ) has a surface area roughly equivalent to that of the wafer ( 30 ).

TECHNICAL FIELD

The present invention relates to method and apparatus for etchingdisk-shaped members, in particular to an etching method and an etchingapparatus for semiconductor wafers.

BACKGROUND ART

A typical method for manufacturing mirror-surface wafers employed as rawmaterial wafers for fabricating semiconductor devices will be explainedbelow. First, a single-crystal semiconductor ingot is grown by theCzochralski method (CZ method) or the floating zone melting method (FZmethod). Because the grown semiconductor ingot is distorted on the outerperiphery thereof, the outer periphery of the semiconductor ingot issubsequently ground in a contour grinding process, e.g. with acylindrical grinding tool, and the outer peripheral shape of thesemiconductor ingot is adjusted. The ingot is then sliced with a wiresaw or the like in a slicing process and machined to obtain disk-shapedwafers with a thickness of about 500-1000 μm, and the outer periphery ofthe wafers is then chamfered in a chamfering process.

Flattening is then conducted by lapping, followed by an etching process,then primary polishing, and secondary polishing. Mirror-surface wafersare then obtained by conducting epitaxial growth process on the wafersurface.

The above-described etching process is carried out for the purpose ofremoving processing-induced distortion that occurred in the previousprocesses, minute defects present on the front and rear surfaces of thewafers, and the matter adhered thereto. An etching apparatus is used foretching the front and rear surfaces of the wafers in the etchingprocess. The conventional etching apparatus will be briefly describedbelow with reference to FIG. 12. FIG. 12 is a longitudinal sectionalview of the conventional etching apparatus, as viewed from the frontsurface thereof.

This etching apparatus mainly comprises an etching chamber 12 filledwith an etching solution, a plurality of rods 16 for supporting androtating a multiplicity of wafers 30, and a housing 10 accommodating thetank and the rods. A plurality of annular wafer support grooves 124 areprovided equidistantly on the circumferential surface of the rods 16,and the outer peripheral sections of wafers 30 are fitted into the wafersupport grooves 124 to hold the wafers 30. On the other hand, the rods16 rotate about the central axis thereof.

With the etching apparatus of such configuration, if the inside of theetching chamber 12 is filled with an etching solution and the rods 16are rotated, the wafers that are in contact by the outer peripherythereof with the rods 16 will also rotate. The etching solution locatedaround the wafers 30 is stirred by the rotation of the wafers 30 and thefront and rear surfaces of the wafers are etched. After such etching hasbeen carried out for a prescribed time, the wafers 30 are taken out fromthe etching apparatus, thereby completing the wafer etching process.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

However, in such conventional etching apparatus, turbulence in solutionoccurs between the wafers due to interaction of the rotating wafers inthe etching process. This turbulence makes a significant contribution tothe degradation of flatness characteristic after etching and degradationof nanotopology by minute undulation.

The present invention was created to resolve the above-describedproblems, and it is an object to provide an etching method and anetching apparatus capable of suppressing turbulence occurring in theetching solution and improve flatness quality and nanotopology qualityafter etching.

In order to attain this object, a first aspect of the present inventionprovides an etching method in which two or more disk-shaped membersimmersed into an etching solution are held in a state where the platesurfaces thereof face each other, and etching is conducted whilerotating the members, wherein a non-rotating member is disposed betweenthe members.

A second aspect of the present invention provides the etching method ofthe first aspect of the invention, wherein the non-rotating member has asubstantially disk shape.

A third aspect of the present invention provides the etching method ofthe first or second aspect of the invention, wherein the surface area ofthe non-rotating member is 95-105% of the surface area of the members.

A fourth aspect of the present invention provides the etching method ofany of the first to third aspect of the invention, wherein the membersare semiconductor wafers.

A fifth aspect of the present invention provides an etching apparatuscomprising an etching chamber filled with an etching solution, and aplurality of rods rotatably supported in contact with the outerperiphery of a plurality of disk-shaped members to rotatably hold themembers in a state where the plate surfaces of the members face eachother, wherein a non-rotating member is arranged in a position betweenthe members held by the member holding means.

A sixth aspect of the present invention provides the etching apparatusof the fifth aspect of the invention, further comprising support columnsfixed parallel to the rods, wherein the non-rotating member is fixed tothe support columns.

A seventh aspect of the present invention provides the etching apparatusof the fifth or sixth aspect of the invention, wherein the non-rotatingmember has a substantially disk shape.

An eighth aspect of the present invention provides the etching apparatusof any of the fifth to seventh aspect of the invention, wherein thesurface area of the non-rotating member is 95-105% of the surface areaof the members.

A ninth aspect of the present invention provides a non-rotating memberfor an etching apparatus comprising an etching chamber filled with anetching solution, and a plurality of rods rotatably supported in contactwith the outer periphery of a plurality of disk-shaped members torotatably hold the members in a state where the plate surfaces of themembers face each other, wherein the non-rotating member is supported onthe rods in place of the members, and a protruding section forpreventing the rotation of the non-rotating member is provided on theouter periphery thereof.

A tenth aspect of the present invention provides the non-rotating memberof the ninth invention, wherein the non-rotating member has asubstantially disk shape.

An eleventh aspect of the present invention provides the non-rotatingmember of the ninth or tenth aspect of the invention, wherein thesurface area of the non-rotating member is 95-105% of the surface areaof the members.

A twelfth aspect of the present invention provides the non-rotatingmember of any of the ninth or eleventh aspect of the invention, whereinthe non-rotating member is made from polypropylene.

A thirteenth aspect of the present invention provides a method formanufacturing semiconductor wafers comprising a step of etching at leasttwo wafers immersed into an etching solution, while holding the wafersso that the plate surfaces thereof face each other and rotating thewafers, wherein a member that changes the flow of the etching solutionbetween every pair of adjacent wafers is arranged.

With the etching apparatus in accordance with the present invention, theflatness of the etched front and rear surfaces of the wafers can beimproved. In particular, the flatness of the front and rear surface inthe vicinity of the wafer center can be improved.

Furthermore, the present invention can be easily employed in theconventional etching apparatus by merely mounting the cell plates in thewafer mounting positions in accordance with the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. l is a longitudinal sectional view of the etching apparatus of afirst embodiment, as viewed from the front surface thereof;

FIG. 2 is a longitudinal sectional view of the etching apparatus of thefirst embodiment, as viewed from the left side surface thereof;

FIG. 3( a) is a longitudinal sectional view of the left support arm 60and left bracket 62, FIG. 3( b) is a longitudinal sectional view of theright support arm 70 and right bracket 72 of the first embodiment;

FIG. 4( a) is a longitudinal sectional view of the barrel of the firstembodiment.

FIG. 4( b) is an enlarged view of section A shown in FIG. 1;

FIG. 5 is a longitudinal sectional view of the etching apparatus of asecond embodiment, as viewed from the front surface thereof;

FIG. 6( a) is a longitudinal sectional view of the left support arm 160and left bracket 162, and FIG. 6( b) is a longitudinal sectional view ofthe right support arm 170 and right bracket 172 of the secondembodiment;

FIG. 7( a) is a longitudinal sectional view of the barrel of the secondembodiment. FIG. 7( b) is a B-B′ sectional view of FIG. 7( a);

FIG. 8( a) is an embodiment of the subject invention showing a cellplate with a large orifice in the middle.

FIG. 8( b) is an embodiment of the subject invention showing a cellplate with a plurality of thin rectangular plates arranged in a row;

FIGS. 9( a)-9(c) show SFQR of the wafers after etching that was found,averaged, and visualized separately for the cases where the cell platewas larger than the wafer, smaller than the wafer, and of about the samesize as the wafer;

FIGS. 10( a)-10(d) show data obtained when etching was conducted on 25wafers by using the conventional etching apparatus and sampling wasconducted from the 25 etched wafers;

FIGS. 11( a)-11 (d) show data obtained when etching was conducted on 20wafers by using the etching apparatus employing the present inventionand sampling was conducted from the 20 etched wafers; and

FIG. 12 is a longitudinal sectional view of the conventional etchingapparatus, as viewed from the front surface thereof.

EXPLANATION FOR REFERNCE NUMERALS

10 . . . housing 10 a . . . side plate 10 b . . . side plate

12 . . . etching chamber 12 a . . . side plate 12 b . . . side plate

14 . . . storage tank

16 . . . rod

18 . . . barrel

20 . . . pump

22 . . . support stand

24 . . . support groove

26 . . . cell plate

28 . . . protruding section

30 . . . wafer

32 . . . gear

34 a . . . gear 34 b . . . gear 34 c . . . gear

34 d . . . gear 34 e . . . gear 34 f . . . gear

35 . . . gear 35 a . . . small gear 35 b . . . large gear

36 . . . drive gear

38 . . . drive motor

40 . . . drive shaft

42 . . . filter

44 . . . pipe

46 . . . discharge pipe

48 . . . discharge valve

50 . . . supply pipe

52 . . . supply valve

60 . . . left support arm

62 . . . left bracket

64 a . . . lid plate 64 b . . . bottom plate

66 . . . air pipe

70 . . . right support arm

72 . . . right bracket

80 . . . box

82 . . . support beam

120 . . . support column

122 . . . cell plate support groove

124 . . . wafer support groove

126 . . . cell plate

128 . . . stopper

160 . . . left support arm

162 . . . left bracket

170 . . . right support arm

172 . . . right bracket

226 . . . cell plate

326 . . . cell plate

BEST MODE FOR CARRYING OUT THE INVENTION

The etching method and etching apparatus in accordance with the presentinvention will be explained below in greater detail with reference tothe appended drawings. The present invention is applicable to variousetching apparatuses where wafers are held parallel to each other, andfor example can be applied to the below-described etching apparatus.However, the description below merely illustrates the modes for carryingout the invention and the present invention is not limited thereto.

EMBODIMENT 1

The first embodiment of the present invention will be described belowwith reference to FIG. 1 to FIG. 4. FIG. 1 is a longitudinal sectionalview of the etching apparatus of the present embodiment, as viewed fromthe front surface thereof. FIG. 2 is a longitudinal sectional view ofthe etching apparatus, as viewed from the left side surface thereof FIG.3( a) is a longitudinal sectional view of a left support arm 60 and aleft bracket 62. FIG. 3( b) is a longitudinal sectional view of a rightsupport arm 70 and a right bracket 72. FIG. 4( a) is a longitudinalsectional view of a barrel. FIG. 4( b) is an enlarged view of section Ashown in FIG. 1.

The entire structure of the etching apparatus will be explained belowwith reference to FIG. 1 to FIG. 4. In this embodiment, a plurality ofwafers 30 are etched after being arranged in a row and mounted on theetching apparatus.

As shown in FIG. 1 and FIG. 2, the etching apparatus of the presentembodiment comprises a box-like housing 10 accommodating all the units,an etching chamber 12 filled with an etching solution, a storage tank 14for recovering the etching solution overflowing the etching chamber 12,a barrel 18 comprising six rods 16 for supporting and rotating thewafers 30, and a pump 20 for circulating the etching solution. Nospecific limitation is placed on the number of rods; it is preferredthat the number of rods be four or more, but three or fewer rods may bealso used.

As shown in FIG. 1, the housing 10 has a box-like structure comprisingfour side plates and one bottom plate. This box-like housing 10accommodates the etching chamber 12 inside thereof. Furthermore, supportstands 22 in the form of thick plates are provided, by one on the leftand right side, in a vertical condition on the top surface of the sideplates 10 a, 10 b of the housing 10. Two straight support holes aredrilled horizontally in each of the mutually opposite surfaces in thetwo support stands 22 shown on the left and right sides of FIG. 1. Thetwo support holes are drilled somewhat above and somewhat below thecenters of each support stand 22. Both end sections of two rod-likesupport beams 82 are inserted into the support holes, and the supportbeams 82 are supported horizontally between the support stands 22.

The support beams 82 that are thus supported horizontally by the supportstands 22 support a left support arm 60 and a right support arm 70 of asubstantially plate-like shape. The left support arm 60 and rightsupport arm 70 are provided in the upper portion and somewhat above thecenter thereof with two through holes having the same diameter as thatof the support beams 82, the two support beams 82 are inserted into thetwo through holes, and the left support arm 60 and right support arm 70are supported by the two support beams 82.

A lid plate 64 a in the form of a flat plate is supported on top of theleft support arm 60 and right support arm 70. Similarly, a bottom plate64 b in the form of a flat plate is supported in the central portions ofthe left support arm 60 and right support arm 70. Sheet materials in theform of flat plates (not shown in the figure) are supported on the frontand rear sides so as to be in contact with the side surfaces of the lidplate 64 a and bottom plate 64 b, and the box-like BOX80 is constitutedby the top portion of the left support arm 60, the top portion of theright support arm 70, sheet materials (not shown in the figure), the lidplate 64 a, and the bottom plate 64 b.

On the other hand, a left bracket 62 with a substantially disk-likeshape is connected to the left support arm 60, so that the plate surfaceof the left support arm 60 and the plate surface of the left bracket 62face each other. Similarly, a right bracket 72 with a substantiallydisk-like shape is connected to the right support arm 70, so that theplate surface of the right support arm 70 and the plate surface of theright bracket 72 face each other. A total of six holes for inserting thesix rods 16 are drilled in the opposing surfaces of the left bracket 62and right bracket 72.

The six cylindrical rods 16 are inserted by one end portion thereof intothe holes drilled in the left bracket 62 and inserted by the other endportion thereof into the holes drilled in the right bracket 72. As aresult, the rods 16 are supported horizontally inside the etchingchamber 12 parallel to the longitudinal direction thereof. A pluralityof ring-like wafer support grooves 24 are provided equidistantly on thecircumferential surface of each rod 16, and the wafers 30 are held byfitting the outer peripheral portions of the wafers 30 into the wafersupport grooves 24.

The six rods 16 are arranged on the circumference of the wafers 30 sothat the wafers 30 can be supported and rotated, as shown in FIG. 4( a).More specifically, four rods are arranged below and two rods arearranged above the positions where the wafers 30 located inside thebarrel 18 have to be loaded. In particular, the six rods 16 arepreferably arranged with a left-right symmetry with respect to thewafers 30.

FIG. 4( b) is an enlarged view of the section A shown in FIG. 1. Asshown in FIG. 4( b), each rod 16 has a support groove 24 having across-sectional shape almost identical to that of the chamfer shape onthe outer periphery of the wafers, and the wafers 30 are supported byfitting the outer periphery of the wafers 30 into the support grooves24. The width of the support groove 24 is preferably larger than thethickness of the wafer 30, and the support 24 is formed so that thewafer 30 is loosely fit into the support groove 24.

As shown in FIG. 3( a), a gear 32 is fixed to the distal end portion ofthe rod 16 inserted into the left bracket 62. A total of five gears 34f, 34 e, 34 d, 34 c, 34 b are arranged vertically from top to bottom inthe successively engaged state on the left support arm 60 (detailedrepresentation of the gears in FIG. 3( a) is partially omitted). A gear35 is arranged in the center of the left bracket 62. In the gear 35, asmall gear 35 is placed on and coaxially connected to a large gear 35 b.The gear 34 b is engaged with the small gear 35 a, and a large gear 35 bis engaged with each gear 32 fixed to one end portion of the rods 16.The six rods 16 are rotated together because all the six gears 32 areengaged with large gears 35 b of the gear 35.

Furthermore, the topmost gear 34 f is engaged with a drive gear 36, andthe drive gear 36 is fixed to a drive shaft 40 of a drive motor 38provided inside the BOX80, as shown in FIG. 1. The rotation of the drivemotor 38 is successively transferred from the drive gear 36 to the gears34 f, 34 e, 34 d, 34 c, 34 b, then to the small gear 35 a of the gear35, and then from the large gear 35 b of the gear 35 to six gears 32.

The drive motor 38 is connected to a control unit (not shown in thefigure) and can provide for rotation in any direction and at any speed.The control unit may be provided inside the BOX80, or may be a controldevice such as a personal computer provided separately from the BOX80.Furthermore, if the control unit is connected to a display, then theinformation relating to the speed or direction of wafer rotation may bedisplayed in a graphical or numerical form on the display, and theoperator may carry out the operations by referring to the displayedinformation, or the control may be conducted automatically according toa program.

As shown in FIG. 3( b), the end portions of rods 16 inserted into theright bracket 72 are supported by the right bracket 72 via guide bushes.As a result, the rods 16 can be smoothly rotated with respect to theright bracket 72. With such a configuration, the rotation of the drivemotor 38 is transmitted to the rods 16 and the rods 16 can be rotated atany speed and in any direction. Furthermore, as described above,rotating the rods 16 at any speed and in any direction makes it possibleto rotate the wafers 30 that are in contact by the outer peripherythereof with the support grooves 24 at any speed and in any direction.

As shown in FIG. 1, in order to support the wavers 30 and cell plates26, the six rods 16 are provided with 16 support grooves 24 with a widthof 1.5 mm and a depth of 2 mm, the pitch of the support grooves 24 being38 mm. A total of 8 wafers 30 and 8 cell plates 26 are alternatelymounted in the form of a lateral stack in which the surfaces of thewafers 30 and cell plates 26 are parallel to each other in the 16support grooves 24.

As shown in FIG. 4( a), the cell plates 26 are thin plates having asubstantially disk shape with a thickness of 0.7-1.5 mm and a diameterof 197-199 mm. Furthermore, the cell plates 26 have two rectangularprotruding sections 28 in the upper and lower portions on the outerperiphery thereof. The protruding sections 28 are fabricated so that thesize thereof matches the width between the rods 16, and when the cellplates 26 are mounted on the support grooves 24, the protruding sections28 hang on the rods 16. The cell plates 26 are mounted inside thesupport grooves 24, similarly to the wafers 30 shown in FIG. 4( b), butbecause the diameter thereof is less than the diameter (200 mm) of thewafers 30, the cell plates are loose inside the support grooves 24. As aresult, even when the rods 16 are rotated, the cell plates 26 do notrotate, and the cell plates 26 are locked so that they cannot rotate ina state of alignment with the positions of the support grooves 24.

In the present embodiment, polypropylene having resistance againstetching solutions is used as a material of the cell plates 26. However,other materials can be also advantageously used, provided they havecertain strength and acid resistance, vinyl chloride being an example ofsuch materials.

On the other hand, as shown in FIG. 2, a box-like storage tank 14 isprovided adjacently to the etching chamber 12. The height of the sideplate 12 a of the etching chamber 12 abutting against of the storagetank 14 is less than the height of the other side plate 12 b, therebymaking it possible to recover the etching solution overflowing theetching chamber 12 into the storage tank 14.

The storage tank 14 is connected to a pump 20 with a pipe 44. A filter42 is provided between the storage tank 14 and the pump 20, and theetching solution flowing out from the storage tank 14 is filtered.Furthermore, a discharge pipe for discharging the spent etching solutionis connected via a discharge valve 48 to the pipe 44 located between thestorage tank 14 and the filter 42. The discharge pipe 46 is connected toa waste solution tank (not shown in the figures) for discarding theetching solution.

A supply pipe 50 for supplying new etching solution is connected via asupply valve 52 to the pipe 44 located between the pump 20 and theetching chamber 12. The etching solution present in the etching chamber12 can be adjusted to the desired concentration by opening the supplyvalve 52 to increase the concentration of the etching solution presentin the etching chamber 12 and closing the supply valve 52 to decreasethe concentration of the etching solution. In this process, the quantityof etching solution supplied to the etching chamber 12 is adjusted to aconstant level by regulating the opening and closing of the dischargevalve 48 according to the quantity of etching solution supplied from thesupply pipe 50.

Furthermore, as shown in FIG. 1, air pipes 66 for blowing air areprovided in the bottom portion of the etching chamber 12. The air pipes66 are provided parallel to the longitudinal direction of the etchingchamber 12, and each air pipe 66 is connected to an air pump (not shownin the figure). Each air pipe 66 comprises holes for air supply that areprovided with the prescribed pitch in the lengthwise direction, and airis supplied to the etching solution located inside the etching chamber12 from those holes.

The operation of the etching apparatus of the above-describedconfiguration will be explained below with reference to FIGS. 1 to 4.

First, the supply valve 52 shown in FIG. 2 is open, and the etchingchamber 12 is filled with the prescribed quantity of the etchingsolution through the supply pipe 50. Any generally used etching solutioncan be employed. For example, a mixed acid obtained by mixing nitricacid, acetic acid, and hydrofluoric acid can be used. The etchingsolution is adjusted to the preset prescribed temperature by thetemperature adjustment mechanism (not shown in the figure).

Then, the operator fits the wafers 30 one by one with pincers into thesupport grooves 24 in the etching device having the cell plates 26mounted thereon in advance and mounts the wafers 30 on the etchingdevice, as shown in FIG. 1. Once the wafers 30 have been mounted, thedrive motor 38 is rotated from the control unit and the rods 16 arerotated. In this case, the rotation of the rods 16 causes the wafersthat are in contact by the outer periphery thereof with the supportgrooves 24 of the rods 16. Controlling the rotation speed of the drivemotor 38 with the control unit makes it possible to rotate the wafers 30at a rate of 10-60 rpm and to change the rotation direction at anysection.

The etching solution present in the storage tank 14 shown in FIG. 2 issupplied to the filter 42 via the pipe 44. The etching solution sent tothe filter 42 is filtered with the filter 42 and then sent to the pump20. The etching solution sent to the pump 20 is pumped to the bottomsection of the etching chamber 12. The pumping rate is adjusted to about40 L/min. As a result, the etching solution present inside the etchingchamber 12 overflows the tank.

The etching solution that overflows the etching chamber 12 is recoveredin the storage tank 14. The etching solution that was recovered in thestorage tank 14 is again pumped by the pump 20 to the bottom portion ofthe etching chamber 12 through the pipe 44 and via the filter 42. Theetching solution thus circulates inside the etching apparatus.

Since the etching solution passes through the filter 42 duringcirculation, foreign matter contained in the etching solution isfiltered out by the filter 42 and the etching solution is maintained ina clean state. Furthermore, because the inside of the etching chamber 12has an ascending flow of the etching solution, the etching solution thatcomes into contact with the front and rear surfaces of the wafers isstirred. As a result, stagnation of the etching solution is prevented,and nonuniform etching of the front and rear surface of the wafers isinhibited.

In this state, the etching of the wafers 30 is conducted for theprescribed replacement time. As a result, the front and rear surfaces ofthe wafers 30 are subjected to target replacement etching. Aftercompletion of the etching, the wafers 30 removed from the etchingchamber 12 are rapidly transferred into a washing tank (not shown in thefigures) and washed.

With the present embodiment, the present invention can be easilyemployed without modifying the conventional etching apparatuses. Thus,the present invention can be easily employed by mounting the cell plates26 and wafers 30 alternately in the support grooves 24 for wafers in theconventional etching apparatus.

EMBODIMENT 2

The second embodiment of the present invention will be described belowwith reference to FIGS. 5 to 7. As described below, a specific featureof the present embodiment is that support columns 120 for fixing thecell plates are provided in the configuration of the first embodiment.Because the two configurations are identical in other aspects, theidentical components will be assigned with the reference symbols of thefirst embodiment and specific explanation thereof will be omitted. Thus,only the support columns 120 and cells plates 126, which represent thedifference between the embodiments, will be explained below.

FIG. 5 is a longitudinal sectional view of the etching apparatus of thepresent embodiment, as viewed from the front surface thereof FIG. 6( a)is a longitudinal sectional view of a left support arm 160 and a leftbracket 162 in the second embodiment of the present embodiment. FIG. 6(b) is a longitudinal sectional view of the right support arm 170 andright bracket 172. FIG. 7( a) is a longitudinal sectional view of thebarrel. FIG. 7( b) is a B-B′ sectional view of FIG. 7( a).

As shown in FIGS. 5 to 7, in the etching apparatus of the presentembodiment, four support columns 120 are fixed parallel to the rods 16to the left bracket 162 and right bracket 172. As shown in FIG. 7( a),the support columns 120 are arranged by two with the prescribed spacingin the vertical direction. As shown in FIG. 7( b), the support columns120 are provided with cell plate support grooves 122 for fixing the cellplates 126 to the support columns 120.

As shown in FIG. 5, a total of 14 cell plate support grooves 122 areprovided with a pitch of 38 mm in each support column 120, those grooveshaving a width of 1.5 mm. By contrast with 16 wafer support grooves 24,there are 14 cell plate support grooves 122 for the reason as follows.

Thus, as shown in FIG. 5, the wafers 30 positioned at both ends of thebarrel 18 face the left bracket 162 and right bracket 172 and do notface other wafers 30 at the surfaces thereof that face to the outside ofthe barrel 18. Therefore, cell plates 126 are not required to bedisposed on the surfaces that do not face other wafers 30. As a result,the cell plate support grooves 122 are disposed on the inner side of thewafer support grooves 24. Furthermore, in the central portion of thebarrel 18, the distance between the wafer support grooves 24 isincreased. Therefore, because the distance between the wafers 30 isincreased, interaction of the wafers 30 during etching is reduced and itis hardly necessary to dispose the cell plates 126. For this reason,cell plate support grooves 122 are not provided in the center of thebarrel 18.

The cell plate support grooves 122 are provided with a half-pitchdisplacement with respect to the wafer support grooves 24. As a result,the cell plate support grooves 122 are arranged so that the wafersupport grooves 24 and cell plate support grooves 122 are locatedalternately in the longitudinal direction of the support column 120.

The cell plates 126 are thin plates with a substantially disk shape andhave a thickness of 1.5 mm and a diameter of 196 mm. Furthermore, asshown in FIG. 7( a), the cell plates 126 have four protruding stoppers128 on the outer periphery thereof. The distal end portion of thestopper 128 has a C-like shape, the inner peripheral portions with theC-like shape are fitted into the cell plate support grooves 122, asshown in FIG. 7( b), and 14 cell plates 126 are fixed to the supportcolumn 120.

In the present embodiment, the diameter of the cell plates 126 is set to196 mm, which is less than the diameter of 200 nun of the wafers 30 inorder to avoid contact of the cell plates 126 with the rod 16. However,the diameter of the cell plates 126 is not limited to this value and maybe equal to the diameter of the wafers 30 or larger than the diameter ofthe wafers 30, but in those cases recesses have to be provided to avoidcontact with the rods 16.

With consideration for the below-described test data, it is preferredthat the diameter of the cell plates be almost equal to the diameter ofthe wafers 30. The advantage of making the cell plates 126 of about thesame size or less than the wafers 30 is that the cell plates 126 do notserve as obstacles when the wafers 30 are mounted with pincers and thewafers 30 can be covered.

The thickness of cell plates 126 is not limited to 1.5 mm, and theeffect of the present invention can be demonstrated with thicker orthinner cell plates. Therefore, thinner plates are generally preferreddue to space saving requirements. However, because strength has to beensured, a thickness of about 0.7-1.5 mm is preferred.

The operation of the etching apparatus of the above-describedconfiguration will be described below with reference to FIGS. 5 to 7.First, similarly to the first embodiment, the etching chamber 12 isfilled with the prescribed quantity of the etching solution.

Then, the operator fits the wafers 30 one by one with pincers into thewafer support grooves 24 and mounts the wafers 30 on the etching device,as shown in FIG. 5. As a result, 16 wafers 30 are arranged in a row witha pitch of 38 mm. Then, similarly to the first embodiment, the wafers 30are rotated at a speed of 10-50 rpm and the rotation direction ischanged after any number of seconds.

The pump is then driven and the etching solution is circulated. In thisstate, the etching of the wafers 30 is conducted for the prescribedreplacement time. As a result, the front and rear surfaces of the wafers30 are subjected to target replacement etching. After completion of theetching, the wafers 30 removed from the etching chamber 12 are rapidlytransferred into a washing tank (not shown in the figures) and washed.

In the first embodiment, the cell plates 26 were fixed to the supportgrooves 24, but with such configuration, half of each support groove 24is used for supporting the cell plate 26. On the other hand, in thesecond embodiment, cell plate support grooves 122 are provided to fixthe cell plates 126 to separate support columns 120, thereby enablingthe increase in productivity. Thus, since the wafer support grooves 24are entirely used for supporting the wafers, the number of wafers thatcan be etched in one cycle is twice as large as that of the firstembodiment.

In the present embodiment, the distance between the wafers and cellplates is halved with respect to that of the first embodiment, but theetching accuracy of the front and rear surfaces of the wafers was notchanged. Therefore, with the present embodiment, the productivity can bedoubled, while maintaining good etching accuracy.

In the above-described first and second embodiment, the explanation wasconducted with respect to the case where all the wafers were rotatedsynchronously. However, a configuration may be also employed in whichthe adjacent wafers are rotated in opposite directions. Furthermore, inthe configurations of the above-described embodiments, the cell plateswere fixed, but a configuration may be also employed in which the cellplates are rotated in the direction opposite that of the wafers.

In the first and second embodiment, the cell plates had a substantiallydisk shape, but no limitation is placed on the shape of the cell plates.For example, cell plates 226 may be used which have a large orifice inthe center, as shown in FIG. 8( a), or cell plates 326 in which aplurality of thin rectangular plates are arranged in a row, as shown inFIG. 8( b), may be also used. Thus, the cell plates may be configured tohave any shape, provided they affect the flow of etching solution.Therefore, though the term “plate” usually refers to a sheet-like body,the term “cell plate” used in accordance with the present inventionrefers not only to a sheet-like body, but also to any body affecting theflow of etching solution.

Furthermore, in the embodiments, the case was explained where an acidmixture was used as the etching solution, but the present invention isalso applicable to the case where alkali etching solutions are used. Anygenerally employed alkali etching solution can be used. For example, anetching solution prepared by mixing sodium hydroxide, isopropyl alcohol,and water can be used.

In the present embodiments, etching of semiconductor wafers wasexplained by way of an example, but it goes without saying that thepresent invention is also applicable to etching of other wafers orthin-sheet bodies, e.g., of metals.

Thus the present invention is not limited to the above-describedembodiments, and the wafer rotation method, shape of cell plates, ortype of etching solution can be modified and changed within the scope ofthe present invention.

Test Data

The case where wafers were etching by using the cell plates of thepresent invention will be explained below in greater detail by takingthe cell plate size as a standard.

The SFQR of wafers after etching was found, averaged and visualized, asshown in FIGS. 9( a)-9(c) separately for the cases of the cell plateslarger than the wafers, smaller than the wafers, and about of the samesize as the wafers.

FIG. 9( a) shows the sub-flatness (SFQR) of the wafers after etchingconducted by mounting cell plates with a surface area 35% larger thanthat of the wafers. Here, the SFQR is one of the indicators of waferflatness. More specifically, it is found by sampling a plurality ofquadrangles (Sites) of the prescribed size (side of 25 mm) from anetched wafer, finding the difference with the desired wafer thickness ofeach sample, and calculating the average value of the values for eachsample. The upper portion of FIG. 9( a) shows the SFQR of each siteobtained by dividing into quadrangles with a side of 25 mm, and thelower portion of FIG. 9( a) shows the visualized SFQR.

Similarly, FIG. 9( b) shows the SFQR of the wafers after etchingconducted by mounting cell plates with a surface area 30% smaller thanthat of the wafers, and FIG. 9( c) shows the SFQR of the wafers afteretching conducted by mounting cell plates of the same size as thewafers.

Three-dimensional graphs obtained by visualization and shown in thelower portions of FIGS. 9( a)-9(c) demonstrate, that the best SFQR ofthe etched wafers is obtained when the cell plates were of about thesame size as the wafers, as shown in FIG. 9( c). Those test dataindicate that the size of the cell plates is preferably about the sameas that of the wafers. In particular, it is preferred that the size ofthe surface area of cell plates be about 95-105% of that of the wafers.Here, the size of the surface area means the projection surface areaobtained by projecting a cell plate on the adjacent wafer. Thus, asshown in FIG. 7( a), the surface area of the overlapping portions of thewafer 30 and cell plate 126 shown by a two-dot-dash line is preferably95-105%.

On the other hand, etching the wafers with the conventional etchingapparatus and with the etching apparatus employing the present inventionwill be compared below by using FIG. 10 and FIG. 11.

FIG. 10 shows data obtained by etching 25 wafers by using theconventional etching apparatus and sampling from 25 etched wafers.

FIG. 10( a) is a graph in which a maximum SFQR in a certain waferssampled of 25 wafers is plotted against the abscissa, and the number ofwafers having this maximum SFQR is plotted against the ordinate.

FIG. 10( b) is a graph in which a SFQR value obtained by sampling SFQRvalues of a total of 1300 sites from 25 wafers is plotted against theabscissa, and the number of sites having this SFQR value is plottedagainst the ordinate.

FIG. 10( c) is a graph showing the average values of SFQR for each siteposition obtained by sampling 25 wafers.

FIG. 10( d) is a graph showing the ration of defected sites with a SFQRof 5 μm or more for each site position, the threshold being 5 μm.

On the other hand, FIG. 11 shows data obtained when etching wasconducted on 20 wafers by using the etching apparatus employing thepresent invention and sampling was conducted from the 20 etched wafers.The graphs and figures in FIGS. 11 (a)-11(d) show the contents similarto that in the corresponding FIGS. 10( a)-11(d).

As shown in FIG. 10( a), the average value of the maximum SFQR valuesfor 25 wafers etched with the conventional etching apparatus is 0.392.On the other hand, as shown in FIG. 11( a), the average value of themaximum SFQR values for 20 wafers etched with the etching apparatusemploying the present invention is 0.256. Thus, using the etchingapparatus employing the present invention improved the average value ofthe maximum SFQR values by no less than 30% with respect to thatobtained with the conventional etching apparatus.

Furthermore, as shown in FIG. 10( b), the average value of the SFQRvalues for 1300 sites sampled from 25 wafers etched with theconventional etching apparatus is 0.205. On the other hand, as shown inFIG. 11( b), the average value of the SFQR values for 1300 sites sampledfrom 20 wafers etched with the etching apparatus employing the presentinvention is 0.130. Thus, using the etching apparatus employing thepresent invention improved the average SFQR value by no less than 35%with respect to that obtained with the conventional etching apparatus.

Furthermore, as shown in FIG. 10( d), in the wafers etched with theconventional etching apparatus, several defected sites with a SFQR of0.5 μm or more appear in the vicinity of the outer periphery of thewafers. By contrast, as shown in FIG. 11( d), absolutely no defectedsites with a SFQR of 0.5 μm or more appeared in the wafers etched withthe etching apparatus employing the present invention.

Thus, the test data shown in FIG. 10 and FIG. 11 demonstrate that usingthe etching apparatus employing the present invention greatly improvesthe flatness of wafers after etching by comparison with that obtained byusing the conventional etching apparatus, and the effect of the presentinvention is especially significant in the vicinity of the wafer center.

1. An etching method in which two or more disk-shaped members immersedinto an etching solution are held in a state where plate surfaces of themembers face each other, and etching is conducted while rotating themembers, Wherein non-rotating member is disposed between the members. 2.The etching method according to claim 1, wherein the non-rotating memberhas a substantially disk shape.
 3. The etching method according to claim1, wherein the surface area of the non-rotating member is 95-105% of thesurface area of the members.
 4. The etching method according to claim 1,wherein the disk-shaped members are semiconductor wafers.
 5. An etchingapparatus comprising: an etching chamber filled with an etchingsolution; and a plurality of rods rotatably supported in contact withouter peripheries of a plurality of disk-shaped members to rotatablyhold the disk-shaped members in a state where the plate surfaces of thedisk-shaped members face each other, wherein a non-rotating memberhaving a substantially disk shape is arranged in a position between thedisk-shaped members held by the rods.
 6. The etching apparatus accordingto claim 5, further comprising support columns fixed parallel to therods, wherein the non-rotating member having the substantially diskshape is fixed to the support columns.
 7. The etching apparatusaccording to claim 5,wherein the surface area of the non-rotating memberis 95-105% of the surface area of the disk-shaped members.
 8. An etchingapparatus comprising: an etching chamber filled with an etchingsolution; a plurality of rods rotatably supported in contact with outerperipheries of a plurality of disk-shaped members to rotatably hold thedisk-shaped members parallel to one another, wherein a non-rotatingmember having substantially disk shape is arranged between twodisk-shaped members, and a protruding section for preventing therotation of the non-rotating member is provided on the outer peripherythereof.
 9. The etching apparatus according to claim 8, wherein thesurface area of the non-rotating member having the substantially diskshape is 95-105% of the surface area of the disk-shaped members.
 10. Theetching apparatus according to claim 8, wherein the non-rotating memberhaving the disk shape is made from polypropylene.
 11. A method formanufacturing semiconductor wafers comprising a step of etching two ormore wafers immersed into an etching solution, while holding the wafersso that the plate surfaces thereof face each other, the etching beingwhile rotating the wafers, wherein a non-rotating member is disposedbetween adjacent wafers.